A digital image sensor utilizes an array of light sensitive cells called pixels. The brighter the light that is incident to a pixel, the greater the charge that accumulates on the pixel. This charge results in a voltage on the pixel that can be sampled and quantized. The brightness of the resulting image is related to the voltage sampled on the pixel. An electronic shutter clears the charge from all the pixels in the array. The exposure time of the image sensor is the time from the clearing of the array to the sampling of it.
Typically, an image sensor uses the same exposure for all pixels in the array. Furthermore, the image sensor typically uses a linear range of pixel devices such that the voltage response of the devices is proportional to the amount of light incident on the devices throughout the dynamic exposure range of the pixel devices.
Every digital image sensor has a dynamic exposure range that is more limited than that of the human eye. Thus, in a high contrast scene, the image captured by the sensor may have the brighter details overexposed or washed out because incident light caused the pixels to exceed the upper end of their dynamic exposure range. Additionally, the image may have the darker details underexposed because the light incident to the pixel did not reach the lower end of their dynamic exposure range. Thus, one may be forced to choose to capture either the detail in dark areas of the scene and leave the light areas over-exposed, or to choose to capture the detail in the light areas of the scene and leave the dark areas underexposed.
In response to this quandary, one solution has been to develop digital image sensors having “high dynamic exposure range” (HDR), which increases dynamic exposure range by combining two or more images taken at different exposure during a time sequence. However, HDR can be difficult to process, for example, in cases where an HDR video is desired. The present application proposes different solutions to increase the dynamic exposure range.
The headings provided herein are merely for convenience and do not necessarily affect the scope or meaning of the terms used.